The present invention relates to communications equipment, and, more particularly, to blind equalization in a receiver.
In blind equalization, the equalizer of a receiver is converged without the use of a training signal. As known in the art, there are two techniques for blind equalization: one is referred to herein as the "reduced constellation algorithm" RCA) (e.g., see Y. Sato, "A Method of Self-Recovering Equalization for Multilevel Amplitude-Modulation Systems," IEEE Trans. Commun., pp. 679-682, June 1975; and U.S. Pat. No. 4,227,152, issued Oct. 7, 1980 to Godard); and the other technique is the so-called "constant modulus algorithm" (CMA) (e.g., see D. N. Godard, "Self-Recovering Equalization and Carrier Tracking in Two-Dimensional Data Communications Systems," IEEE Trans. Commun., vol. 28, no. 11, pp. 1867-1875, November 1980; and N. K. Jablon, "Joint Blind Equalization, Carrier Recovery, and Timing Recovery for High-Order QAM Signal Constellations", IEEE Trans. Signal Processing, vol. 40, no. 6, pp. 1383-1398, 1992.) Further, the co-pending, commonly assigned, U.S. patent application of Werner et al., entitled "Blind Equalization," Ser. No. 08/646404, filed on May 7, 1996, presents an new blind equalization technique--the multimodulus algorithm (MMA)--as an alternative to the above-mentioned RCA and CMA approaches.
Unfortunately, whether using the RCA, CMA, or MMA, approaches, the ability to blindly converge the equalizer is also affected by the number of symbol levels represented in the signal point constellation. In other words, the difficulty of "opening the eye" (as this term is used in the art) increases when the number of symbol levels increases.